ADU Rules: Santa Monica vs Topanga
How do adu rules rules compare between Santa Monica, CA and Topanga, CA?
Santa Monica and Topanga have similar restriction levels.
Santa Monica, CA
Los Angeles County
Santa Monica regulates ADUs under SMMC §9.31.025. Maximum size is 650 sq ft on lots up to 6,000 sq ft or 800 sq ft on larger lots. No development fees. Ministerial approval process.
View full Santa Monica rules →Topanga, CA
Los Angeles County
Topanga is an unincorporated CDP in Los Angeles County governed by LA County Code Title 22 §22.140.640 (Accessory Dwelling Units and Junior Accessory Dwelling Units), most recently amended April 2024. Detached ADUs are capped at 1,200 sq ft; multifamily-lot ADUs have no maximum size under county rules. Topanga lies within the Santa Monica Mountains Coastal Zone, so a Coastal Development Permit also applies.
View full Topanga rules →Key Facts Comparison
| Fact | Santa Monica | Topanga |
|---|---|---|
| Code Section | SMMC §9.31.025 | - |
| Max Size (small lot) | 650 sq ft (lots ≤6,000 sf) | - |
| Max Size (large lot) | 800 sq ft (lots >6,000 sf) | - |
| Setbacks | 4 feet rear/side (new) | - |
| Dev Fees | None | - |
| Governing Code | - | LA County Code §22.140.640 |
| Single-Family | - | 1 ADU + 1 JADU per lot |
| Multifamily Detached | - | Up to 2 new + conversion ADUs |
| Coastal Permit | - | Required (Santa Monica Mtns LCP) |
| Side/Rear Setback | - | 4 ft (new construction) |
Highlighted rows indicate differences between cities.
Santa Monica FAQ
Can I build an ADU on my property in Santa Monica?
Santa Monica regulates ADUs under SMMC §9.31.025. Maximum size is 650 sq ft on lots up to 6,000 sq ft or 800 sq ft on larger lots. No development fees. Ministerial approval process.
What are the size limits for an accessory dwelling unit in Santa Monica?
Code Section: SMMC §9.31.025. Max Size (small lot): 650 sq ft (lots ≤6,000 sf). Max Size (large lot): 800 sq ft (lots >6,000 sf). Setbacks: 4 feet rear/side (new).
Topanga FAQ
Who regulates ADUs in Topanga?
Topanga is unincorporated, so LA County Department of Regional Planning regulates ADUs under LA County Code Title 22 §22.140.640, not a separate city ordinance.
Do I need a Coastal Development Permit for a Topanga ADU?
Yes. Topanga falls within the certified Santa Monica Mountains Local Coastal Program, so most ADU construction requires a Coastal Development Permit in addition to the building permit.
Can a Topanga multifamily lot add detached ADUs?
Yes. Under LA County Code §22.140.640, multifamily lots may add up to two detached new-construction ADUs plus conversion ADUs within non-livable space (up to 25% of existing units).
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